The present invention relates to an apparatus for forming an elongated synthetic resin plate or sheet.
The method of forming a synthetic resin plate can generally be divided into a press method according to which a granular or powdery resinous starting material is introduced to between molding plates or into a box-like metal mold, and is heated and cooled under the application of pressure, and an extrusion method according to which a metal mold having an oblong shape in cross section is connected to an extruder, and a molten resinous starting material is continuously extruded by the extruder through the metal mold, followed by cooling. With the former press method, the heating and cooling are repetitively performed, wasting large amounts of heat. To produce elongated synthetic resin plates or sheets, furthermore, the products formed by pressing must be connected by welding. Therefore, the press method requires increased number of manufacturing steps, increased labor, and results in inefficient produceability. With the latter extrusion method on the other hand, residual strain builds up in the resinous raw material in the direction of extrusion, the resulting products find very limited applications, and further, the metal molds must be provided according to thicknesses of the products. The extrusion method therefore requires tremendous costs.
There has also been proposed an improved molding method of the type which utilizes double steel belts, in which the resinous starting material of which the thickness is adjusted to a predetermined thickness is supplied to between the upper steel belt and the lower steel belt, and the resinous material is heated under the application of pressure via the steel belts, followed by cooling.
The above method is an improvement of the aforementioned press method, and is effective for improving the produceability. The press mechanism for pressing the resinous starting material employed by this method consists of heating and cooling rollers that are rotatably arrayed on the steel belt, in order to press the starting material as the rollers rotate on the belt.
With this method in which the steel belt is heated or cooled by the rollers, however, the rollers and the steel belt come into line contact. In other words, the contacting areas are very small, and the heat conductivity is small. Further, it is technically difficult to apply high pressure onto the resinous starting material from the rollers via steel belt. Accordingly, the above improved method is capable of producing only limited kinds of products such as foamed resin plates.
Moreover, since there is no member that defines the right and left sides of the steel belt, the side edges of the raw material collapses when the resinous raw material is heated and melted in the heating zone, resulting in losses of raw material. Further, since the product has no definite width, selvages must be cut away in a subsequent step.
The object of the present invention is to provide an apparatus for forming a synthetic resin plate or sheet having any desired thickness, in which the heat conductivity to the double steel belts is increased. The increased pressure is exerted on the resinous starting material, and members that define the right and left sides of the steel belt are provided to reduce losses of the staring materials and to increase the operation efficiency, while eliminating the aforementioned defects inherent in the conventional double steel belt-type molding method.
The molding apparatus of the present invention is characterized in that the lower steel belt is placed on a lower board and is intermittently fed by a predetermined distance. Side frames are installed on the lower steel belt, the side frames stretching on both the right and left edges of the lower steel belt in the lengthwise direction thereof. The upper steel belt is disposed between said two side frames, an upper board is installed on the upper steel belt, either one of the upper board or the lower board is so constructed as to move up and down. The resinous starting material is pressed by the pressing operation of the board which moves up and down via the upper and lower steel belts, and the upper and lower boards are divided into a plurality of blocks so as to correspond to the opposing ones, thereby constituting heating zones having heating means and cooling zones having cooling means.
The upper board may be constructed to be movable so that the pressing operation is performed when it lowers, or the lower board may be constructed to be movable so that the pressing operation is performed when it rises.
The heating zone may be composed of a single block in which the pressing force and the heating temperature are maintained constant. Preferably, however, the heating zone should be composed of a plurality of blocks having different pressing forces and heating temperatures. It is also allowable to provide a heat-insulating block for maintaining the ripened condition of the resinous starting material.
The cooling zone is also made up of a single block or a plurality of blocks having different pressing forces and cooling temperatures.
As required, the plurality of blocks forming the boards should be arrayed maintaining a suitable gap relative to each other. This helps prevent the steel belts from being folded at acute angles by the boards and stepped portions that develop among the neighboring blocks due to the thermal expansion or contraction of the starting material being caused by the temperature differential, and hence, the steel belts are protected from being damaged or broken.
When the upper or lower moving board has finished the pressing operation, the lower steel belt is moved by one block to transfer the resinous starting material to the next block. The upper steel belt, however, may be maintained stationary or, preferably, be moved by a distance of the same block in synchronism with the lower steel belt.
Side frames prevent the right and left side edges of the resinous raw material from being collapsed. Under the condition in which the resinous raw material is compressed by the moving board, the moving board or the upper steel belt should be in sliding contact with the inner surfaces of the side frames, since the pressing mold is established by the side frames and the board or the steel belt. A good fitting condition is obtained by the moving board and the side frames; the upper steel belt is arrayed by maintaining a slight gap relative to the side frames so that it can be smoothly transferred.
The right and left side frames should be provided by maintaining a small gap relative to the lower steel belt, so that the lower steel belt can be smoothly transferred. For this purpose, the side frames should be so supported on the lower board so as to move up and down, and should protrude onto the lower steel belt. Further, springs should be interposed between the board and the side frame thereby to maintain a small gap between the steel belt and the side frames.
Although a small gap is formed between the side frames and the lower steel belt, the moving board moves up or down during the pressing operation to close the small gap; therefore, the resinous starting material does not leak.
For this purpose, the side frames should be forcibly pressed onto the lower board via the lower steel belt before the resinous starting material is being compressed.
The side frames can be effectively lowered by a knock pin or a spring incorporated in the upper board.